The term "wired, packet-based. baseband LAN" is intended to mean a LAN, or LAN segment, in which the LAN transmission medium (for example, twisted pair wiring, coaxial cable) is adapted to carry electrical signals and in which the data being transferred between stations is transmitted over the transmission medium in packets using baseband signalling techniques. Such wired, packet-based, baseband LANs are referred to below as LANs of the "aforesaid type".
LANs of the aforesaid type may use various media access control techniques including CSMA/CD, token passing and slotted ring but all have the general characteristic that signals are normally only present on the LAN when user data or control data is being transferred - that is, no signals are normally present in the gaps between packets ("inter-packet" gaps).
The majority of faults on LANs of the aforesaid type are very simple and are typically caused by the failure of a particular component such as a network node, spanning device (bridge), or the wires or cables (or their terminators) themselves. In diagnosing network faults, it is therefore useful to be able to make simple observations of the state of any particular segment of a LAN.
It is an object of the present invention to provide apparatus which by simple measuremnts, can substantially facilitate fault diagnosis on LANs of the aforesaid type.